MOLECULAR ORBITAL ESTIMATION OF REDUCED PARTITION FUNCTION RATIOS OF LITHIUM IONS IN ION EXCHANGER PHASE OF AQUEOUS ION EXCHANGE SYSTEMS

Satoshi Yanase1, Takao Oi2

1Residential Systems and Materials Laboratory, Asahi Kasei Corporation, 1-3-1 Yakoh, Kawasaki, Kanagawa 210-0863, Japan,
2Department of Chemistry, Sophia University, 7-1 Kioicho, Chiyoda, Tokyo 102-8554, Japan

Structures of Li+(H2O)5SO3--R with -R representing the methyl and other groups modeling the lithium ion in the ion exchanger phase of aqueous ion exchange systems were optimized based on the molecular orbital theory and the reduced partition function ratios (RPFRs) for the 6Li/7Li isotope substitutions were estimated. The structure around the lithium ion was nearly unchanged by the substitutions of the methyl group by the other groups. Correspondingly, the RPFR value did not vary substantially, either; the maximum decrease of 0.0008 was observed for -R = -C(C2H5)3 from that of -CH3. It was indicated that the equilibrium constant of the lithium isotope exchange reaction between the ion exchanger and the external solution phases could change by ca. 0.001 without any substantial structural change around the lithium ion in the ion exchanger phase. It was also indicated the ONIOM calculation is effective when treating isotope effects of large molecules.